The envelope above the layer of molten hydrogen expands under the influence of heat, causing the star to “swell”. It becomes less dense, therefore less hot, and then emits more and more towards the red color, hence the name “red giant”.

This swelling effect makes red giants very bright, furthermore, due to their large size, their oscillations are relatively slow. These two elements make it easy to observe their photometric variations. “It is easy to observe something Whose flow varies Glowing slowly and adequately, that’s why we chose to target the red giants“, Explains Benoit Moser, professor at the Paris Observatory and co-author of the publication.

In addition, thick discs will carry remnants of the very young Milky Way, which will have older stars on average than thin discs. Scientists have actually realized that the Milky Way is made up of a thin disk around our heart, which is part of our solar system, but also of a thick disk, which extends further. These two components of the galaxy have very different dynamics and history.

Dating the stars of the galaxy to understand its formation

Formed 13 billion years ago, our galaxy then merged three billion years later with an ancient dwarf satellite galaxy called Gaia-Enceladus, then similar in size to the Magellanic Clouds. Understanding the impact of this important event in the evolution of the galaxy will allow us to predict the future of the galaxy or even a future similar to its own.

“If we want to know what our galaxy will look like tomorrow, we have to Understand What did she look like yesterday This is the goal of galactic archeology, we do it like digging, but looking at the distant stars “, Benoit Moser explains.

So it is trying to date some of the oldest stars in our galaxy that scientists at the University of Birmingham are studying the chronology of the galaxy’s formation. “Of Stars form in a galaxy much earlier, but a large event such as a collision with another galaxy is not absolutely neutral in its evolution, so interest in dating it “, Continue Benoit Moser.

Stellar science examines the internal structure of stars

Scientists have been able to estimate the age of these stars by studying the vibrations of red monsters and their chemical composition. In fact, combined with spectroscopy, which makes it possible to reduce the chemical composition of a star, asteroscismology provides much more accurate results than other dating methods.

“looking at Very fine variations in stellar photometry, we find that this stellar flow modifies over time. These modulations reflect the way stars vibrate, and these vibrations depend on very direct parameters. Important As Mass, Rayon orEvolutionary state Stars”, Comments Benoit Moser.

It became a discipline in 2000 when it was demonstrated that all stars, like the Sun, have oscillation modes, this involves measuring the frequencies and amplitudes of natural oscillations of the stars. These measurements then allow scientists to gather information about the size and mass of the star, examine its internal structure, and then extract its age from this information.

Josephina Montalban of the School of Physics and Astronomy at the University of Birmingham, and the first author of the article, states in a statement: “The chemical composition, location, and speed of stars seen today in the Milky Way provide valuable information about their origin. As our knowledge of when and how these stars formed grows, we can better understand how the accretion of Gaia-Enceladus by the Milky Way affected the evolution of our galaxy. “